This invention relates to fixturing to support a gas turbine component, and more specifically, to clamping the gas turbine component in the fixture and shaping the root of the gas turbine component.
In the most commonly practiced approach, turbine blades for gas turbine engines are cast to approximately the final shape. Then portions of the turbine blade, such as the root and the shroud, if any, are shaped to the final desired form by a technique such as grinding. The turbine blade is thereafter processed by depositing protective coatings or by other procedures.
The finished turbine blades are assembled into a turbine disk or wheel, with a xe2x80x9cdovetailxe2x80x9d form on the root of each turbine blade engaging a respective conformably shaped slot on the turbine disk. The turbine disk is in turn supported on a shaft in the gas turbine engine. The turbine blades must have precisely established positions and angular orientations in the turbine disk. Any mispositioning and misorientation may lead to aerodynamic inefficiency and the introduction of unacceptable vibrations in the turbine disk and the turbine blade as the turbine disk turns during service.
Because it is the root of each turbine blade that engages the slot on the turbine disk, the root must be shaped very precisely. Two techniques have been widely used to hold the turbine blade in an exact location and orientation for the shaping of the root. In one, the airfoil of the turbine blade is cast into a matrix of a metal with a low melting point, which is used to hold the turbine blade with its root positioned for grinding or other shaping. This approach, while operable, requires that the low-melting-point metal be cleaned from the surface of the airfoil after the shaping of the root is completed. Even traces of the metal remaining after careful cleaning of the surface of the airfoil may adversely affect the subsequent application of the coatings. Mechanical fixtures or jigs have been developed to hold the turbine blade. These fixtures avoid the use of the low-melting-point metal, but have not been fully satisfactory because they misposition the root or because they do not hold the turbine blades sufficiently repeatably and securely so that each root is shaped the same.
There is a need for an improved approach to the shaping of the roots of turbine blades and other gas turbine components. The present invention fulfills this need, and further provides related advantages.
The present invention provides a fixture for holding a gas turbine component in a specific fixed position for the shaping of the gas turbine component, and a method for performing the shaping. The approach does not use a molten metal whose complete removal is difficult. The fixture holds the gas turbine component using features of the gas turbine component that have been previously precisely established. This approach allows the gas turbine components to be processed precisely, quickly, reproducibly, without contamination, and with minimal dependence upon operator skill.
A fixture is provided for clamping a gas turbine component, such as a turbine blade, a compressor blade, or in some cases a vane, having a root separated from an airfoil by a transversely extending platform having an upper side adjoining the airfoil and a lower side adjoining the root, and a tang at an end of the root remote from the platform and the airfoil. The fixture comprises a base upon which the remainder of the fixture is supported, and a stop which prevents the gas turbine component from moving past a stop limit when the gas turbine component is forced in a clamping direction extending between the root and the airfoil. Two clamp arms are provided, including a first clamp arm on a leading-edge side of the gas turbine component with a first clamp surface facing the gas turbine component, and a second clamp arm on a trailing-edge side of the gas turbine component with a second clamp surface facing the gas turbine component. Each clamp arm is movable, preferably by a pivoting movement on the base, between a released position in which its clamp surface does not contact the platform and a clamped position in which its clamp surface contacts the platform and forces the gas turbine component in the clamping direction and against the stop. A clamping force source, preferably in the form of an hydraulic cylinder, controllably moves each of the clamp arms between the released position and the clamped position.
In the preferred embodiment, a pressure surface on each side of the root of the gas turbine component engages a respective shoulder of the fixture that defines the stop. In the normal practice, the pressure surfaces have been previously precisely shaped in reference to the remainder of the gas turbine component. Shaping the balance of the gas turbine component, specifically the lower end or tang of the gas turbine component, in reference to the pressure surfaces ensures that the entire root will be properly shaped and have the pressure surfaces and root mutually shaped for proper orientation of the airfoil.
The clamp surfaces of the clamp arms are desirably shaped to be conformable to a portion of the platform that is contacted by the clamp surface when the clamp arm is in the clamped position. This conforming shape maximizes the uniformity of the transfer of the clamping force into the gas turbine component and the security and stability of the clamping, with minimal risk of damage to the underside of the platform.
A method for shaping a gas turbine component comprises the steps of furnishing a gas turbine component, such as a turbine blade, having a root separated from an airfoil by a transversely extending platform having an upper side adjoining the airfoil and a lower side adjoining the root, and a tang at an end of the root remote from the platform. A fixture as described previously, in its basic or modified forms, is furnished. The gas turbine component is clamped in the fixture, and thereafter the root of the gas turbine component is shaped while the gas turbine component is clamped in the fixture. Preferably, the tang portion of the root, and/or an end surface of the root, is shaped by grinding.
The present approach provides a convenient, secure fixturing approach which avoids the use of molten metal and also ensures that the gas turbine component is properly positioned for shaping of the root, particularly the tang of the root.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.